Colonoscopy is an essential procedure for the early diagnosis of colorectal conditions; however, over 60% of patients undergoing non-sedated colonoscopy report moderate to severe pain. This study aims to investigate the central analgesic mechanisms of transcutaneous electrical nerve stimulation based on wrist-ankle acupuncture theory (TENS-WAA). A multimodal approach combining electroencephalography (EEG) and functional near-infrared spectroscopy (fNIRS) will be employed to assess pain-related brain activity, with artificial intelligence applied to model the relationship between objective neurophysiological signals and subjective pain experience.

This is a single-centre, randomised, double-blind, controlled trial involving 60 patients undergoing colonoscopy without anaesthesia. Participants will be randomly allocated (1:1) to either an electrical stimulation group receiving TENS-WAA or a sham stimulation group. EEG and fNIRS data will be acquired before, during and after the procedure. The primary outcome is the analysis of EEG-fNIRS signals to characterise cerebral responses associated with pain modulation. Secondary outcomes include patient-reported pain using the Visual Analogue Scale (VAS), total colonoscopy duration and the correlation between EEG-fNIRS indicators and VAS scores. A deep learning framework will be used to enhance pain prediction accuracy.

This study has received ethical approval from the Ethics Committee of Changhai Hospital, Shanghai (approval reference CHEC2025-006), and has been registered at ClinicalTrials.gov. Written informed consent will be obtained from all participants. Findings will be disseminated in peer-reviewed academic journals and at relevant scientific conferences, regardless of outcome, contributing to evidence-based, non-pharmacological pain management strategies.

ClinicalTrials.gov, NCT06813703.